Landslide vulnerability of the Debre Sina-Armania road section, Central Ethiopia: Insights from geophysical investigations

Abstract

Geophysical investigations using 2D electrical imaging and magnetic methods have been conducted to study the landslide problem on the road located at Dokakit Kebele near Sar Amba Kidane Mhiret locality between Debre Sina and Armania towns in Central Ethiopia. From field observations, the landslide problem in the Debre Sina-Armania road section at Dokakit is due to a combination of factors, the most important of which are topography, the high degree of weathering, hydrology of the area, and human activities. Among these factors, human activities that include deforestation for housing, agricultural activities, search for building materials, and road construction are generally assumed to be the triggering factors for slope failure in the area. From the interpretation of the geophysical results, the near-surface geology of the study area is found to be composed of massive deposits of fragmented basalts and structurally disturbed layers together with expansive clay soils, which considerably contribute to the sliding problem. Another contributing factor to the subsurface instability is the high gradient slope in the area and the lack of vegetation/wooded tree cover. From the geophysical survey results, it has further been possible to map zones of weakness in the subsurface over which the geologic layers slide as well as their vertical and lateral extents. Areas of active sliding surfaces and extensive subsurface cracks, especially at the two ends of the profiles, were mapped. A combination of numerous weak zones, deep weathering conditions of the lithologic units, the action of rainfall, springs, and the high slope gradient of the study area were the contributing factors for this sliding problem. Remedial measures to stabilize a section of the affected area and construction of a detour road are proposed as mitigation measures for the road segment's recurrent and rather expensive failure over the locality.